Apparatus for fabricating a conformal thin film on a substrate

ABSTRACT

An apparatus for fabricating a conformal thin film on a substrate are disclosed. The apparatus includes a top shield having a top surface and a bottom surface and a bottom shield having an aperture formed therein and a thickness. The bottom shield is coupled to the bottom surface of the top shield such that the top shield covers the aperture. The apparatus further includes a substrate holder that may hold a substrate. The substrate holder is in contact with the bottom shield such that a reaction chamber is formed having a volume defined by the aperture and the thickness of the bottom shield.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. b10/706,637, filed Nov. 12, 2003 and entitled “METHOD AND APPARATUS FORFABRICATING A CONFORMAL THIN FILM ON A SUBSTRATE” now U.S. Pat. No.______.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to film deposition, and moreparticularly to an apparatus for fabricating a conformal thin film on asubstrate.

BACKGROUND OF THE INVENTION

Atomic layer deposition (ALD), also known as sequential pulsed chemicalvapor deposition (SP-CVD), atomic layer epitaxy (ALE) and pulsednucleation layer (PNL) deposition, has gained acceptance as a techniquefor depositing thin and continuous layers of metals and dielectrics withhigh conformality. In an ALD process, a substrate is alternately dosedwith a precursor and one or more reactant gases so that reactions arelimited to the surface of a substrate. Uniform adsorption of precursorson the wafer surface during the ALD process produces highly conformallayers at both microscopic feature length scales and macroscopicsubstrate length scales, and achieves a high density of nucleationsites. These attributes result in the deposition of spatially uniform,conformal, dense and continuous thin films.

Although ALD techniques support deposition of conformal thin layers, adrawback of the technique is the low average deposition rate, which isrelated to the need to repeat several cycles having finite durations.For example, the repeated cycle of precursor and reactant adsorption andthe intervening chamber purges is time consuming, which results inreduced throughput relative to conventional deposition techniques.Specifically, an ALD sequence includes at least two purge pulses andthese purge pulses are typically the most time consuming portion of theALD sequence. Therefore, improvements in ALD equipment have focused ontechniques to decrease the time needed to complete a purge pulse.

The most logical solution to decreasing the duration of the purge pulseis to flow the purge gas at higher speeds through the reactor, which maybe achieved by increasing the flow rate of the purge gas. Typical flowrates used in the industry are several standard liters per minute (SLM)(e.g., approximately 2.5 SLM) at pressures of between approximately 0.2and approximately 20 Torr. These flow rates lead to substantially highergas flow speeds than obtained in conventional CVD processes.

One of the effects of increasing purge gas flow speed is the occurrenceof turbulence in the gas injector. Typically, the turbulence occurs inan expansion zone of a gas injector near an inlet used to supply thepurge gas. Turbulence in the expansion zone may cause the flow patternof the purge gas across a conventional diffuser plate to be altered.Specifically, the fraction of the total flow passing through theopenings in the diffuser plate located near the turbulent zone decreasessignificantly. The decrease in gas flow through openings near theturbulent zone when compared to the gas flow through openings locatedaway from the turbulent zone may create an uneven distribution ofprecursor during a doping pulse, which ultimately forms a non-uniformfilm on a substrate. Additionally, recirculation of gas in the expansionzone caused by the turbulence leads to inefficient purging of theprecursors from the expansion zone, which may cause gas phase reactionsthat form a powder in the expansion zone.

SUMMARY OF THE INVENTION

In accordance with the present invention, the disadvantages and problemsassociated with fabricating conformal thin films on a substrate havebeen substantially reduced or eliminated. In a particular embodiment, anapparatus for fabricating conformal thin films on a substrate isdisclosed that include a diffuser plate having a protrusion that reducesturbulence in an expansion volume associated with a gas injector.

In accordance with one embodiment of the present invention, a method forfabricating conformal thin films on a substrate includes introducing agas from a gas inlet into an expansion volume associated with an atomiclayer deposition (ALD) system. The gas is flowed through a diffuserplate adjacent to the expansion volume and a reaction chamber. Thediffuser plate includes a protrusion located opposite the gas inlet,which reduces turbulence in the expansion volume.

In accordance with another embodiment of the present invention, anapparatus for fabricating conformal thin films on a substrate includes areaction chamber and a gas injector located adjacent to the reactionchamber. The gas injector includes an expansion volume and a gas inletfor introducing a gas into the expansion volume. A diffuser plate islocated adjacent to the expansion volume and the reaction chamber. Aprotrusion that reduces turbulence in the expansion volume is locatedadjacent to the diffuser plate and opposite the gas inlet.

In accordance with a further embodiment of the present invention, anapparatus for fabricating conformal thin films on a substrate includes areaction chamber and a gas injector located adjacent to the reactionchamber. The gas injector includes an expansion volume and a gas inletfor introducing an inert gas into the expansion volume. A diffuser platelocated adjacent to the expansion volume and the reaction chamberincludes a bevel that is located opposite the gas inlet, and reducesturbulence and gas phase reactions in the expansion volume.

Important technical advantages of certain embodiments of the presentinvention include a diffuser plate that suppresses turbulence in a gasinjector over a wide range of flow rates. The diffuser plate includes aprotrusion located opposite a gas inlet of a gas injector. Theprotrusion prevents gas flowing from the gas inlet from bouncing off thesurface of the diffuser plate and recirculating in an area around thegas inlet. The protrusion, therefore, facilitates laminar gas flow in anexpansion volume of a gas injector associated with an ALD system.

Another important technical advantage of certain embodiments of thepresent invention includes a diffuser plate that increases throughput ofan ALD system. The diffuser plate includes a protrusion that facilitateslaminar gas flow throughout an expansion volume of a gas injector. Thelaminar gas flow allows the gas during a purge pulse of an ALD processto remove residual precursor from the expansion volume. By moreeffectively removing the precursor, gas phase reactions during asubsequent purge pulse may be reduced or even eliminated, thusdecreasing the frequency of cleaning processes.

A further important technical advantage of certain embodiments of thepresent invention includes a diffuser plate that uniformly distributes aprecursor in a reaction chamber. During a doping pulse, a precursorcombined with a gas may be flowed through the diffuser plate. Aprotrusion on the diffuser plate facilitates a laminar gas flow withinan expansion volume. Because gas/precursor mixture flows in a laminarmanner within the expansion volume, the gas/precursor mixture flows moreuniformly through openings in the diffuser plate. The uniform flow ofthe mixture provides for an improved distribution of precursor over asubstrate in the reaction chamber and ultimately allows a substantiallyuniform film to be formed on the substrate.

All, some, or none of these technical advantages may be present invarious embodiments of the present invention. Other technical advantageswill be readily apparent to one skilled in the art from the followingfigures, descriptions, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete and thorough understanding of the present embodimentsand advantages thereof may be acquired by referring to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numbers indicate like features, and wherein:

FIG. 1 illustrates an atomic layer deposition (ALD) system for forming aconformal thin film on a substrate according to teachings of the presentinvention;

FIGS. 2A and 2B illustrate flow patterns in a gas injector at differentflow rates using a conventional diffuser plate;

FIGS. 3A and 3B illustrate flow patterns over a substrate at differentflow rates using a conventional diffuser plate;

FIG. 4 illustrates an example embodiment of a gas injector associatedwith an ALD system according to teachings of the present invention;

FIG. 5 illustrates another example embodiment of a gas injectorassociated with an ALD system according to teachings of the presentinvention;

FIGS. 6 a and 6 b respectively illustrate a top view and a bottom viewof an example embodiment of a diffuser plate including protrusionsformed on a top surface according to teachings of the present invention;and

FIG. 7 illustrates a gas injector flow pattern using a beveled diffuserplate according to teachings of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention and their advantages arebest understood by reference to FIGS. 1 through 7, where like numbersare used to indicate like and corresponding parts.

The conceptual groundwork for the present invention involves an atomiclayer deposition (ALD) process to create highly conformal thin films. Inan ALD process, individual precursors are pulsed onto the surface of asubstrate contained in a reaction chamber, without mixing the precursorsin the gas phase. Each precursor reacts with the surface of thesubstrate to form an atomic layer in such a way that only one layerforms at a time. The introduction of the precursor into the reactionchamber may be known as a doping pulse. In between doping pulses, thereaction chamber may be purged by flowing a gas over the substrate. Thetime needed to complete the doping and purge pulses may depend on theflow rate of the precursor or the purge gas. In conventional ALDsystems, the precursor or purge gas flows from a gas injector, through adiffuser and into the reaction chamber. The diffuser may include a flatsurface having multiple openings to allow the precursor or purge gas toflow into the reaction chamber. If the flow rate of the purge gas duringthe purge pulse is above a specific level, turbulence may occur near thegas inlet in the injector. The present invention provides a protrusionassociated with the diffuser that reduces and even eliminates turbulencein the gas injector. The protrusion may be located opposite the gasinlet such that the purge gas flows over the protrusion and through theopenings in the diffuser in a more uniform manner.

FIG. 1 illustrates atomic layer deposition (ALD) system 10 for forming aconformal thin film on a substrate. In the illustrated embodiment, ALDsystem 10 includes diffuser plate 12, gas lines 14 a and 14 b (generallyreferred to as gas lines 14), gas injector 16, reaction chamber 18 andoutlet 20. During a purge pulse, a gas may flow through one or both ofgas lines 14 a and 14 b from gas reservoirs. The gas then flows throughdiffuser plate 12 included in gas injector 16. A protrusion may belocated opposite the gas inlet. The protrusion functions to direct thegas within gas injector 16 such that the gas flows in a laminar mannerover a wide range of flow rates.

ALD system 10 may include one or more gas reservoirs (not expresslyshown) connected to gas injector 16 by gas lines 14. In one embodiment,the reservoirs may contain an inert gas that is used to remove precursorfrom gas injector 16 during a purge pulse and/or that is combined with aprecursor during a doping pulse. In another embodiment, the reservoirsmay contain a precursor used during a doping pulse. Gas lines 14 mayfeed the gas into gas injector 16. In one embodiment, gas lines 14 maybe formed of stainless steel and have a diameter of approximateone-quarter (¼) inch. Although the illustrated embodiment shows aparticular number of reservoirs and associated gas lines, ALD system 10may include a single reservoir and gas line or more than two reservoirsand their corresponding gas lines.

Reaction chamber 18 may contain substrate holder 19. In one embodiment,a substrate placed in substrate holder 19 may be a p-type or n-typesilicon substrate. In other embodiments, the substrate may be formedfrom gallium arsenide or any other suitable material that may be used asa substrate on which one or more layers of material may be deposited.The one or more layers deposited by ALD system 10 may form films used tofabricate conformal barriers, high-k dielectrics, gate dielectrics,tunnel dielectrics and barrier layers for semiconductor devices. ALDfilms are also thermally stable and substantially uniform, which makesthem attractive for optical applications. Another potential applicationfor ALD is the deposition of AlO_(x) as a gap layer for thin film heads,such as heads for recording densities of 50 Gb/in² and beyond thatrequire very thin and conformal gap layers. Additionally, ALD thin filmsmay be used to form structures with high aspect ratios, such asMicroElectroMechanical (MEM) structures.

The thin film may be formed on a substrate by alternately flowing one ormore precursors combined with an inert gas (e.g., a doping pulse) andthe inert gas (e.g., a purge pulse) through reaction chamber 18. Theprecursor may react with the surface of the substrate to form a singlelayer of film. The doping and purge pulses may be repeated until a thinfilm having the desired thickness is formed on the substrate. During thepulses, the gas and precursor may be removed from reaction chamber 18through outlet 20 by a pump (not expressly shown).

During the purge pulse, the gas from the reservoirs expands into an areacontained in gas injector 16. In conventional ALD systems, if the flowrate of the gas is high enough (e.g., greater than approximately 500sccm), turbulence may occur due to the flat surface of a diffuser platelocated opposite the gas inlet of gas injector 16. The turbulenceprevents the gas in a purge pulse from completely clearing the precursorfrom gas injector 16 because the precursor may be trapped in theturbulence, which may lead to gas phase reactions during subsequentpulses that form a powder in gas injector 16. As described below inreference to FIG. 2B, the turbulence may decrease the total flow of gaspassing through openings in the diffuser plate located near theturbulent zone.

In the present invention, the expansion volume located in gas injector16 may include a protrusion located opposite the gas inlet. In oneembodiment, the protrusion may be integral to diffuser plate 12 locatedbetween gas injector 16 and reaction chamber 18. In another embodiment,the protrusion may be separate from diffuser plate 12 and mounted to oneof the walls associated with gas injector 16.

In one embodiment, the protrusion may be beveled and the surfacesforming the bevel may have similar or different slopes. In otherembodiments, the protrusion may include several sloped segments havingdifferent slopes or a surface with a smoothly varying slope. Theprotrusion functions to reduce and even eliminate turbulence at typicalgas flow rates (e.g., approximately 2500 sccm and greater) for an ALDprocess by directing the flow of the gas through gas injector 16 suchthat the flow is uniform through each of the openings in the diffuserplate. Additionally, the protrusion may prevent gas phase reactions fromoccurring in gas injector 16 because the purge pulse more effectivelyremoves the precursor from gas injector 16.

FIGS. 2A and 2B illustrate flow patterns inside of a gas injector atdifferent flow rates using a conventional diffuser plate. Specifically,FIG. 2A illustrates the flow pattern of a gas inside gas injector 30 ata flow rate of approximately 100 sccm. A gas may be introduced into gasinjector 30 through gas inlet 32. At the low flow rate, the gas flowssubstantially uniformly over diffuser plate 34. As shown, no turbulenceis present due to the low flow rate and the gas may flow throughopenings 36 in a uniform manner.

However, as illustrated by FIG. 2B, at a flow rate of approximately 500sccm (e.g., a rate approximately five times greater than the rateillustrated in FIG. 2A), turbulent zones may occur near gas inlet 32.The turbulence causes a drop in pressure, which causes the flow throughopenings 36 located opposite gas inlet 32 to be lower than openings 36located away from gas inlet 32. In some cases, if the pressure in thegas injector near the turbulent zones is lower than the pressure in thereaction chamber, the gas may actually be sucked from the reactionchamber into the gas injector. The different flow through openings 36may cause an uneven distribution of the precursor during the dopingpulse. Additionally, the recirculation in the turbulent zones may leadto inefficient purging of the precursor in gas injector 30, which maycause gas phase reactions that produce powder in gas injector 30. Thepowder may damage the substrate contained in the reaction chamber andcreate a need to clean the ALD system more often.

FIGS. 3A and 3B illustrate flow patterns over a substrate at differentflow rates using a conventional diffuser plate. Specifically, FIG. 3Ashows the flow pattern of a gas above a substrate (not expressly shown)at a flow rate of approximately 133 sccm as calculated by a commerciallyavailable computational flow dynamics software (e.g., software developedand sold by CFDRC corporation of Huntsville, Ala.). As illustrated, thegas flows substantially uniformly from gas injector 40 over thesubstrate to outlet 42. FIG. 3B shows the flow pattern of the gas at aflow rate of approximately 1333 sccm (e.g., a rate approximately tentimes greater than the flow rate illustrated in FIG. 3A). As shown, thegas flow over the substrate is substantially different at the higherflow rate, especially in the region directly opposite the gas inlet (notexpressly shown) in gas injector 40. As described above in reference toFIG. 2B, a conventional diffuser plate may induce turbulence in theregion of gas injector 40 near the gas inlet. As shown in FIG. 3B, theturbulence may reduce the amount of gas flowing through the openings inthe diffuser plate that are located opposite the gas inlet. Thedifference in the flow pattern through the openings in the diffuserplate may cause non-uniform distribution of the precursor over thesubstrate.

FIG. 4 illustrates an example embodiment of a diffuser plate including aprotrusion located opposite a gas inlet in a gas injector associatedwith an ALD system. Gas line 14 may include fast valving system 51located near gas inlet 53 of gas injector 16. Fast valving system 51 mayinclude several subcomponents, such as mass flow controllers and on/offvalves to control the flow versus time profiles of the dosing and purgepulses. A gas may flow through fast valving system 51 into expansionvolume 52 via gas inlet 53. The flow of gas from expansion volume 52 toreaction chamber 18 may be restricted by diffuser plate 12. In oneembodiment, diffuser plate 12 may be a metal plate including at leastone opening 56. The number, size and position of openings 56 may beselected to obtain uniform precursor flow in reaction chamber 18 duringa doping pulse and uniform gas flow during a purge pulse. Diffuser plate12 may further be disposable since prolonged use may lead to depositionof the precursor in openings 56 and subsequent alteration of flowcharacteristics over time.

In the illustrated embodiment, diffuser plate 12 includes protrusion 58located opposite gas inlet 53. Protrusion 58 may direct the gas flowinginto expansion volume 52 such that the gas flows uniformly through eachof openings 56 into reaction chamber 18 through openings 56. The heightof protrusion 58 may scale with the size of gas inlet 53 and a desiredoperation range for the flow rate. In general, the size of gas inlet 53and the flow rate may depend on the size of the substrate, as largeramounts of precursor may be used for larger substrates. In oneembodiment, the substrate may have a diameter of approximately 150millimeters and protrusion 58 may have a height between approximatelythree millimeters (3 mm) and approximately eight millimeters (8 mm).

Protrusion 58 may include surfaces 57 and 59 that form a bevel. In theillustrated embodiment, surfaces 57 and 59 may have approximately thesame length and slope. In other embodiments, one of surfaces 57 and 59may have a larger slope and/or length than the other surface. In afurther embodiment, protrusion 58 may be formed in the shape of aninverted “U” such that the surface of protrusion 58 has a smoothlyvarying slope. In yet another embodiment, protrusion 58 may include morethan two sloped segments where the sloped segments have the same ordifferent slopes and lengths.

Surface 57 may form a first angle (Φ₁) with respect to the surface ofdiffuser plate 12 and surface 59 may form a second angle (Φ₂) withrespect to the surface of diffuser plate 12. In one embodiment, thefirst and second angles (Φ₁ and Φ₂) may be between approximately thirtydegrees (30°) and approximately sixty degrees (60°). The first andsecond angles (Φ₁ and Φ₂) may be approximately equal or one of theangles may be greater or less than the other angle.

Protrusion 58 functions to direct the gas flow toward openings 56 indiffuser plate 12 such that the amount of gas flowing through each ofopenings 56 is approximately equal. Protrusion 58 may further functionto eliminate turbulence in expansion volume 52 by preventing the gasfrom bouncing off of the surface of diffuser plate 12 towards gas inlet53, which further prevents recirculation from occurring near gas inlet53. By eliminating recirculation of the gas in expansion volume 52, theprecursor may be more efficiently purged from expansion volume 52 duringthe purge pulse, which reduces the possibility of gas phase reactionsthat may form a powder in expansion volume 52 after prolonged use of ALDsystem 10.

In another embodiment, protrusion 58 may be separate from diffuser plate12. Protrusion 58 may be mounted in expansion volume 52 such thatprotrusion 58 is located opposite gas inlet 53. For example, protrusion58 may be located on a post mounted to one of the walls of expansionvolume 52. The post may have a width or diameter less than or equal tothe base of protrusion 58. Additionally, the post may have a shapesimilar to that of protrusion 58 in order to further aid the flow of gasin expansion volume 52.

In a further embodiment, a wall protrusion, similar to protrusion 58located on diffuser plate 12, may be formed on at least one of the wallsforming expansion volume 52. The wall protrusion may be formed on atleast one of the walls in order to provide a more uniform gas flowthrough expansion volume 52 and to further reduce turbulence at higherflow rates. The wall protrusion may have one or more surfaces. In oneembodiment, the surfaces may have approximately the same lengths and/orslopes. In other embodiments, the surfaces of the wall protrusion mayhave different lengths and/or slopes. In further embodiments, thesurface of the wall protrusions may form an inverted “U”.

FIG. 5 illustrates another example embodiment of a diffuser plateincluding a protrusion located opposite a gas inlet in a gas injectorassociated with an ALD system. In the illustrated embodiment, gas inlet53 may be located at the top of expansion volume 52, rather than thecenter as illustrated in FIG. 4. Diffuser plate 12 may includeprotrusion 60 that functions to direct the gas flow toward the bottom ofexpansion volume 52. In another embodiment, protrusion 60 may beseparate from diffuser plate 12 and formed on the wall of expansionvolume 52. Protrusion 60 may form an angle (Φ) with respect to thesurface of diffuser plate 12 of approximately thirty degrees (30°) toapproximately sixty degrees (60°). Protrusion 60 may allow the gas flowto be evenly distributed through openings 56 such that a precursor isevenly distributed in reaction chamber 18.

Although protrusion 60 is illustrated as having a single surfaceadjacent to a wall of expansion volume 52, protrusion 60 may also havemultiple surfaces. For example, gas inlet 53 may be located in aslightly asymmetrical position relative to the walls of expansion volume52. Protrusion 60 may include at least two surfaces, where the surfaceextending toward the larger portion of expansion volume 52 may have agreater length than the surface extending toward the smaller area ofexpansion volume 52.

FIGS. 6 a and 6 b respectively illustrate a top view and a bottom viewof an example embodiment of diffuser plate 12 including protrusions 58 aand 58 b. As illustrated in FIG. 1, ALD system 10 may include gas lines14 a and 14 b. Each of gas lines 14 a and 14 b may include acorresponding gas inlet and when diffuser plate 12 is used in ALD system10, protrusions 58 a and 58 b may be respectively located opposite thegas inlets for gas lines 14 a and 14 b. In this example, protrusions 58a and 58 b may respectively prevent turbulence from forming near the gasinlets associated with gas lines 14 a and 14 b. In other embodiments,diffuser plate 12 may include any suitable number of protrusions 58 suchthat at least one protrusion is located opposite each of the gas inletsassociated with the expansion volume of a gas injector.

As shown in FIG. 6 a, diffuser plate 12 includes two rows of openings 56formed on a front surface. As described above in reference toprotrusions 58 a and 58 b, the two rows of openings 56 may correspond tothe number of gas inlets associated with the expansion volume. In otherembodiments, diffuser plate 12 may include one row or greater than tworows of openings 56 where the number of rows depends on the number ofgas inlets associated with the expansion volume of the gas injector.

As shown in FIG. 6 b, diffuser plate 12 may include chamber openings 54formed on a back surface. Chamber openings 54 may be located adjacent toreaction chamber 18 when diffuser plate 12 is included in ALD system 10illustrated in FIG. 1. In order to ensure that the precursor and gasenters reaction chamber 18 through each one of openings 56 at the samelocation, openings 56 may be interleaved in diffuser plate 12 to form asingle row of chamber openings 54. In the illustrated embodiment,openings 56 may be formed in diffuser plate 12 at a forty-five degreeangle with respect to the normal of the surface of diffuser plate 12. Inother embodiments, openings 56 may be formed in diffuser plate 12 at asuitable angle such that each of openings 56 forms a singlecorresponding chamber opening 54. In a further embodiment, the number ofrows of chamber openings 54 formed on a back surface of diffuser plate12 may be equal to the number of rows of openings 56 formed on a frontsurface of diffuser plate 12.

FIG. 7 illustrates a gas injector flow pattern using a beveled diffuserplate. In the illustrated embodiment, the flow rate is approximately8000 sccm. As shown, protrusion 58 may facilitate a laminar gas flow ata flow rate approximately sixteen (16) times greater than the flow rateat which the conventional diffuser plate illustrated in FIG. 2B showssignificant turbulence. The gas, therefore, may be evenly distributedthrough each of openings 56 and the precursor distribution in reactionchamber 18 may be improved.

Although the present invention has been described with respect to aspecific preferred embodiment thereof, various changes and modificationsmay be suggested to one skilled in the art and it is intended that thepresent invention encompass such changes and modifications fall withinthe scope of the appended claims.

1. An atomic layer deposition (ALD) apparatus for fabricating aconformal thin film on a substrate, comprising: a top shield including atop surface and a bottom surface; a bottom shield including an apertureformed therein and a thickness, the bottom shield coupled to the bottomsurface of the top shield such that the top shield covers the aperture;a substrate holder operable to hold a substrate, the substrate holder incontact with the bottom shield such that a reaction chamber is formedhaving a volume defined by the aperture and the thickness of the bottomshield; and a diffuser plate including a protrusion operable tofacilitate an increased flow rate of a gas supplied by at least oneinlet to the reaction chamber, the diffuser plate removably coupled tothe top surface of the top shield.
 2. The apparatus of claim 1, whereinthe volume of the reaction chamber is slightly greater than a substratevolume.
 3. The apparatus of claim 1, further comprising the diffuserplate including at least one opening operable to receive the gas fromthe at least one inlet for introduction into the reaction chamber. 4.The apparatus of claim 3, further comprising the protrusion operable tofacilitate uniform gas flow through the at least one opening in thediffuser plate.
 5. The apparatus of claim 1, further comprising avertical shield removably coupled to a top shield side surface and abottom shield side surface, the vertical shield including an outletformed therein operable to be coupled to a pump such that the pumpremoves the gas introduced into the reaction chamber and providesuniform gas flow over the substrate.
 6. The apparatus of claim 1,further comprising the top shield removably coupled to the bottomshield.
 7. An atomic layer deposition (ALD) apparatus for fabricating aconformal thin film on a substrate, comprising: a top shield including atop surface and a bottom surface; a bottom shield including an apertureformed therein and a thickness, the bottom shield removably coupled tothe bottom surface of the top shield such that the top shield covers theaperture; a substrate holder operable to hold a substrate, the substrateholder in contact with the bottom shield such that a reaction chamber isformed having a volume defined by the aperture and the thickness of thebottom shield; a diffuser plate including a bevel operable to facilitatean increased flow rate of a gas supplied by at least one inlet to thereaction chamber, the diffuser plate removably coupled to the topsurface of the top shield; and a vertical shield including an outletformed therein operable to be coupled to a pump for removing the gasintroduced into the reaction chamber, the vertical shield removablycoupled to a top shield side surface and a bottom shield side surface.8. The apparatus of claim 7, wherein the volume of the reaction chamberis slightly greater than a substrate volume.
 9. The apparatus of claim7, further comprising the diffuser plate including at least one openingoperable to receive the gas from the at least one inlet for introductioninto the reaction chamber.
 10. The apparatus of claim 9, furthercomprising the bevel operable to facilitate uniform gas flow through theat least one opening in the diffuser plate.
 11. The apparatus of claim7, wherein the aperture comprises a rectangular shape.
 12. An atomiclayer deposition (ALD) apparatus for fabricating a conformal thin filmon a substrate, comprising: a top shield including a top surface and abottom surface; a bottom shield including an aperture formed therein anda thickness, the bottom shield coupled to the bottom surface of the topshield such that the top shield covers the aperture; and a substrateholder operable to hold a substrate, the substrate holder in contactwith the bottom shield such that a reaction chamber is formed having avolume defined by the aperture and the thickness of the bottom shield.13. The apparatus of claim 12, wherein the volume of the reactionchamber is slightly greater than a substrate volume.
 14. The apparatusof claim 12, further comprising: a diffuser plate including at least oneopening operable to receive a gas from at least one inlet forintroduction into the reaction chamber, the diffuser plate coupled tothe top surface of the top shield; and a vertical shield including anoutlet formed therein operable to be coupled to a pump for removing thegas introduced into the reaction chamber, the vertical shield coupled toa side surface of the top shield and a side surface of the bottomshield.
 15. The apparatus of claim 14, further comprising the diffuserplate removably coupled to the top surface of the top shield such thatthe diffuser plate may be disposed.
 16. The apparatus of claim 14,further comprising the diffuser plate including a protrusion locatedopposite the inlet, the protrusion operable to facilitate an increasedgas flow rate to the reaction chamber.
 17. The apparatus of claim 16,further comprising the protrusion operable to facilitate uniform gasflow through the at least one opening in the diffuser plate.
 18. Theapparatus of claim 14, further comprising the gas selected from thegroup consisting of a precursor, a reactant gas and an inert gas. 19.The apparatus of claim 12, wherein the aperture comprises a rectangularshape.
 20. The apparatus of claim 12, further comprising the top shieldremovably coupled to the bottom shield.